A polytrimethylene terephthalate (hereinafter referred to as PTT) fiber have been known in the prior documents such as J. Polymer Science: Polymer Physics Edition Vol. 14, pages 263 to 274 (1976) or Chemical Fibers International Vol. 45, pages 110 to 111 April (1995).
These documents describe a basic characteristic of a stress-strain property of the PTT fiber; that is, the PTT fiber is low in initial modulus and excellent in elastic recovery, which is suitable for clothing and carpet use.
Japanese Examined Patent Publication No. 43-19108, Japanese Unexamined Patent Publication Nos. 11-189923, 2000-239927 and 2000-256918, and EP1059372A disclose a side-by-side type composite fiber containing PTT as one component or two components thereof.
These prior documents disclose that a side-by-side type or an eccentric sheath-core type composite fiber in which PTT is used as at least one component thereof (hereinafter referred to as a PTT composite fibers) have a latent crimpability, and the crimps develop by heat treatment, and exhibit a favorable stretchability and a soft touch.
According to the study of the present inventors, although products obtained from the PTT composite fibers are excellent in stretchability and softness, problems have been found in the post-treatment process such as knitting/weaving or dyeing and the uniformity of dyed product as described in items I, II and III below:
I. Troubles in Knitting/Weaving Process
As the preparation prior to the knitting/weaving, a warping process is employed before the knitting process, and a warp preparation process and a twist yarn preparation process are employed before the weaving process.
When the PTT composite fiber is used in a warp-knitting process, “opening of single filaments” may occur due to the tension fluctuation during the knitting operation, whereby the adjacent fibers are interfered with each other to result in filament breakage.
When a twist yarn is formed of the PTT composite fibers and used for producing a woven fabric, there is a problem in that white powder may be generated during the twisting and/or weaving process and is deposited on guides in the passage to result in the yarn breakage.
FIG. 1 is a simplified illustration of a photograph of the PTT composite fiber surface after being twisted and twist-set by wet heat observed by a scanning electronic microscope. It will be apparent from FIG. 1 that white powder is generally uniformly deposited on the surface of single filament.
FIG. 2 is an example of a chart obtained by measuring white powder deposited on a tension control guide of a loom in accordance with a differential scanning calorimetry (DSC).
This curve exhibits endothermic peaks at about 230° C. and about 250° C. The peaks at about 230° C. and at about 250° C. coincide with the melting temperature of PTT and that of a cyclic dimer of trimethylene terephthalate, respectively. Accordingly, it is apparent that the white powder deposited on a guide or others is PTT or trimethylene terephthalate cyclic dimer which is a by-product of the former.
The higher the crimpability of the developed crimps and the more of a number of twist, the more the white powder is derived from PTT. If the number of twists is 1000 T/m or more, the frictional abrasion of the twist yarn becomes so significant that an abrasive trace can be observed by a scanning electronic microscope. Thus, the PTT composite fiber is difficult to use as a high twist yarn.
Also, the higher the twist-setting temperature after being twisted, the more the white powder is derived from the cyclic dimer of trimethylene terephthalate.
While it is not apparent why such white powder is generated, one reason may be the following:
PTT composite fiber, especially that having a high stretchability, has not only latent crimpability but also developed crimps developed prior to being heat-treated; in other words, it is characterized as having apparent crimpability. It is surmised that such a side-by-side type composite fiber having developed crimpability is significantly higher in contact resistance with guides or others in the preparation process of knitting/weaving than that having non-developed crimpability to result in the generation of white powder.
Also, it is surmised that during the twist-setting process after twisting, trimethylene terephthalate cyclic dimer contained in a PTT composite fiber separates out from the fiber interior to the surface thereof to cause white powder.
There is a proposal in WO99/39041 to eliminate the yarn breakage during the spinning or false-twist texturing process by imparting PTT fiber with a special finishing agent. However, there is no description therein of the PTT composite fiber having the developed crimpability wherein crimps are developed.
Also, in the above prior document, there is no disclosure of the problem of the entanglement of fibers during the knitting process or the generation of white powder during the knitting/weaving process, much less the disclosure or suggestion of a solution thereto.
II. Troubles in Dyeing Process
It is known that, besides fabric dyeing or print dyeing, a dyed knit/woven fabric may be obtained by a yarn-dyeing method.
Since a pattern is formed in the knit/woven fabric obtained by the yarn-dyeing method wherein colors of the respective fibers are different from each other, a high-grade fashionable product results.
While the yarn-dyeing method includes hank dyeing or cheese dyeing, the latter is mainly used nowadays because of the dyeing economy thereof.
The knit/woven fabric obtained from the cheese-dyed PTT composite fibers more easily develops crimps during the dyeing process in comparison with a false-twist textured yarn of PTT or polyethylene terephthalate (hereinafter referred to as PET). Accordingly, if the cheese-dyed PTT composite fibers are used for the knit/woven fabric, there is a feature in that the favorable stretchability is obtained due to high crimps.
Contrary to such a feature, it has been found that, when the PTT composite fibers are cheese-dyed, oligomer extracted from the fiber is deposited on the dyed cheese to deteriorate the dyeing uniformity.
That is, when a dyeing liquid circulates from inside of the cheese to outside thereof, oligomer separated out from the PTT composite fibers is dissolved in the dye liquid and deposited on the fiber. The portion of the fiber on which the oligomer is deposited causes an uneven dyeing or a loss of color clarity. Dyeing troubles caused by oligomer are not limited only to cheese dyeing but also appear in fabric dyeing.
According to analysis by the present inventors, it has been found that a main component of the oligomer is a cyclic dimer of trimethylene terephthalate.
Although the reason is not apparent why a large amount of cyclic dimer is separated out from the PTT composite fibers, it is surmised that a low PTT orientation in the PTT composite fibers allows the cyclic dimer to move toward the fiber surface.
Japanese Patent No. 3204399 discloses a PTT fiber and refers to the content of oligomer in the PTT fiber for the purpose of restricting the contamination of orifices in a spinneret. However, the content is high and there is no disclosure at all of white powder being generated during the twisting, heat-setting and weaving of PTT composite fibers or oligomer troublesome in the dyeing process thereof.
Thus, PTT composite fibers free from troubles in the dyeing process are strongly desired.
III. Dyeing Uniformity
The dyeing uniformity of a PTT composite fiber product is an important factor.
It has been found that the following two problems deteriorate the dyeing uniformity when the PTT composite fibers are industrially produced.
One of the problems is the yarn bending. If the difference in intrinsic viscosity between two polymers used is made to be larger for the purpose of improving the stretchability and the stretchback property of the resultant composite fibers, yarn bending is generated due to the difference in melting viscosity between the two polymers extruded from an orifice during the spinning, which causes fiber size fluctuation in the lengthwise direction of the resultant composite fiber.
The other of the problems is the contamination of the orifice from which the melted polymer is extruded. When the PTT is spun, polymer may deposit on the periphery of the orifice as the spinning time passes to result in the contamination so-called “eye mucus”. This contamination is peculiar to PTT, and the larger the difference in intrinsic viscosity between the two polymers, the more significant this phenomenon becomes. It has been found that when the “eye mucus” generates, the extruded fiber becomes uneven (because of the generation of a so-called “jerk”) not only to reduce the spinning stability but also increase the fiber size fluctuation U % of the composite fibers obtained. A fabric obtained from the PTT composite fibers having a large fiber size fluctuation is unevenly dyed to largely lower the product grade.
To solve the problem of yarn bending, a spinning method is proposed, in Japanese Examined Patent Publication (Kokoku) No. 43-19108, BP 965,729 and Japanese Unexamined Patent Publication (Kokai) No. 2000-136440, using a spinneret having orifices in which flow paths for two polymers are slanted.
Since the prior art disclosed in these documents, however, is a system in which two polymers having the difference in intrinsic viscosity are extruded from an orifice directly after they meet together, if the difference in melting viscosity between the two polymers is large, it is impossible to sufficiently prevent the deviation of a flow of melted polymer, and as a result, the fiber size fluctuation is not suppressed enough.
Accordingly, it is strongly desired that PTT composite fibers free from yarn breakage during the knitting/weaving process and having high stretchability, high stretchback property and dyeing uniformity, and a method for the production thereof, are developed.